Description:

Objective:

My proposed research will evaluate the effect of containment caps on mercury methylation processes in contaminated sediments. In-situ sediment caps are passive barriers that separate contaminated sediment from the overlying water and influence geochemical conditions in the underlying sediment. Mercury methylation occurs primarily in the bottom sediments of aquatic environments and the complex geochemical changes induced by cap placement will impact the mobility and fate of mercury.

The objective of this research is to evaluate the biogeochemical changes induced by cap placement and to examine how these changes will affect mercury methylation. In situ capping physically sequesters contaminated sediments from overlying water, reducing or eliminating the flux of organic matter and nutrients to the underlying sediment and driving the entire sediment layer anaerobic. In order to assess the effectiveness of containment capping strategies, the consequent effects on the complex processes controlling mercury methylation must be evaluated.

Approach:

The research needs identified above will be studied in an integrated research program, the overall goal of which is to evaluate the utility of sediment caps to eliminate the release of methylmercury to surficial sediments and the overlying water. Laboratory tests will be used to complement mathematical modeling of geochemical processes in order to understand the changes induced by cap placement. Microelectrodes will be used with microprofiling equipment to monitor concentrations of important nutrients and redox conditions in laboratory microcosms. Sulfide has recently been shown to control the bioavailability of mercury and an emphasis will be placed on understanding the mercury-sulfide system. An existing mathematical model which simulates sediment geochemistry will be refined and calibrated using data from laboratory work and extended to include mercury methylation processes.

Expected Results:

It is widely accepted that sulfate reducing bacteria are responsible for the bulk of mercury methylation in aquatic sediments. Consequently, it is expected that cap-induced changes to the extent and location of sulfate reduction will be directly related to changes in mercury methylation. The results of this research will provide practical information about the effects of capping on methylation processes which can be used to guide remediation efforts.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.